Abstract
The security of drinking water is a serious issue in China and worldwide. As the backup source of drinking water for the Changde City in China, the Huangshi Reservoir suffers from the threat of eutrophication due to the water quality of the reservoir ecosystem being affected by the tributaries that carry Non-Point Source (NPS) pollutants. The calculation of the water environmental capacity (WEC) can provide a scientific basis for water pollution control, which refers to the maximum amount of pollutants that the water can accommodate. In this paper, according to the hydrological characteristics of the river–reservoir combination system, a one-dimensional (1-D) water quality model and the Environmental Fluid Dynamics Code (EFDC) model were chosen to calculate the water environmental capacity of each functional zone in this basin. The quantity control of pollution from the tributaries was conducted based on the combined results of the water environmental capacity calculation from the EFDC model and a one-dimensional (1-D) river water quality model. The results show that total water environmental capacity of the tributaries included a chemical oxygen demand (COD) of 421.97 tons; ammonia nitrogen (NH3-N) of 40.99 tons; total nitrogen (TN) of 35.94 tons; and total phosphorus (TP) of 9.54 tons. The water environmental capacity of the Huangshi Reservoir region accounts for more than 93% of the total capacity. The reduction targets of the major pollutants in the Huangshi Reservoir and its four major input rivers, which are, namely, the Bamao River, the Longtan River, the Fanjiafang River, and the Dongtan River, have been determined to achieve the water quality objectives for the reservoir in 2020 and 2025. The results will be helpful for the local water quality management and will provide a valuable example for other similar water source reservoirs.
Highlights
In recent years, instead of flood control and irrigation, drinking water supplementation has become the primary purpose of reservoirs in China [1]
In order to simulate the water environmental capacity (WEC) and control the amount of pollution of the Huangshi Reservoir with multiple tributaries in 2020 and 2025, we developed an integrated method to evaluate the WEC of the river–reservoir combination system, which consisted of the coupling of the 1-D model and the Environmental Fluid Dynamics Code (EFDC)
The equation for calculating the WEC was derived based on a 1-D convection-diffusion equation, with the adopted model expressed as follows [5]: M = (CS − C0 exp(−kL/u))exp(kL/2u) Qr where M is the water environmental capacity per unit time (t); Cs is the pollutant concentration of the tail section in mg/L; C0 is the pollutant concentration of the initial section in mg/L; k is the pollutant degradation coefficient in 1/s; and L is the length of the reach
Summary
Instead of flood control and irrigation, drinking water supplementation has become the primary purpose of reservoirs in China [1]. With the enormous development of aquaculture, water pollution in reservoirs has become a serious problem with the water quality of drinking water source directly influencing people’s health, which is related to the economic development and stability of the general social situation. The water environmental capacity (WEC) refers to the maximum amount of pollutants that the water can accommodate under the designed hydrological conditions and the specified environmental objectives without destroying its own function [4,5]. Most case studies mainly use a river [12,15,16,19,23], lake, and reservoir [6,14,20,22] as objects in China, but there has been less research on the WEC of a certain river–reservoir combination system
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